1. Field of the Invention
The present invention relates to isolated polypeptides having 5-aminolevulinic acid synthase activity and isolated nucleic acid sequences encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the nucleic acid sequences as well as methods for producing and using the polypeptides.
2. Description of the Related Art
Heme, a chelate complex of protoporphyrin IX and iron, serves as a prosthetic group of hemoproteins. Protoporphyrin IX consists of a porphyrin ring, substituted with four methyl groups, two vinyl groups, and two propionic acid groups, which acquires an iron atom to form heme. The biosynthesis of heme from glycine and succinyl-CoA involves eight enzymatic steps. The first enzyme in the biosynthetic pathway is 5-aminolevulinic acid synthase.
The conversion of an apoprotein into a hemoprotein depends on the availability of heme provided by the heme biosynthetic pathway. The apoprotein form of the hemoprotein combines with heme to produce the active hemoprotein. The active hemoprotein acquires a conformation which makes the hemoprotein more stable than the apoprotein to proteolytic attack. If the amount of heme produced by a microorganism is less relative to the amount of the apoprotein produced, the apoprotein will accumulate and undergo proteolytic degradation lowering the yield of the active hemoprotein.
In order to overcome this problem, Jensen showed that the addition of heme or a heme-containing material to a fermentation medium led to a significant increase in the yield of a peroxidase produced by Aspergillus oryzae (WO 93/19195). While heme supplementation of a fermentation medium results in a significant improvement in the yield of a hemoprotein, it is non-kosher, costly, and difficult to implement on a large scale.
The overexpression of a gene in the heme biosynthetic pathway of a cell provides an alternative approach for overcoming this problem.
The cloning and sequencing of a 5-aminolevulinic acid synthase gene from Aspergillus nidulans (Bradshaw et al., 1993, Current Genetics 2233:501-507) have been disclosed.
It is an object of the present invention to provide new polypeptides having 5-aminolevulinic acid synthase activity and genes encoding same.